Packet bursts are a common issue in today's high speed wireless data networks such as High-Speed Downlink Packet Access (HSDPA) and result from the way such networks are implemented. A TCP server or proxy sending data to a mobile client over a wireless data network can receive sudden bursts of TCP acknowledgement packets. These bursts are caused by buffering TCP acknowledgement packets in the uplink path. Buffering of TCP acknowledgment packets is a side effect of the way high speed data networks are implemented and is required primarily to maintain the order while delivering TCP packets. Such bursts of TCP acknowledgment packets can also be caused by radio channel fading. Radio channel fading is due to a number of reasons, such as atmospheric interference, distance between the mobile unit and the cell tower transceivers, and so on.
In reaction to a burst of TCP acknowledgements, a TCP server typically sends a burst of data packets to the mobile client in order to fill up the congestion window as defined by the TCP protocol. In most cases, it is desirable to have the server send data as fast as possible to the client in order to use the full channel bandwidth. Nodes in the Wireless Packet Core Network, however, are typically not designed to handle bursty transmissions and frequently drop packets when a burst of TCP/IP packets are received in a short interval of time.
A TCP server assumes that a packet is lost if the acknowledgement from the client is not received within a configured time interval, or if it receives one or more duplicate acknowledgements from the client. In either case, the server has to re-transmit the lost packets and this triggers TCP's slow start and congestion avoidance algorithms. The end result is that the full channel bandwidth is not utilized. The inefficient use of the available wireless channel bandwidth is particularly common when a large amount of data is transferred from a server to a mobile client. For example, this problem would be common during large file downloads using HTTP or FTP.
A large burst of TCP acknowledgement packets from the mobile client immediately following network fade triggers a burst of data packets from the TCP server. As stated above, a large data packet burst from the TCP server usually results in undesirable packet loss and inefficient use of the wireless data channel.